Plastic Keymat

Plastic Keymat also called as P+R keypad, plastic rubber keymat, plastic and rubber keypad.

Plastic keymat design guide provides designers with a high-level overview of all the factors to consider when incorporating a plastic rubber keymat into a product. The Design Guide includes the material choice, surface symbols guideline, keymat structure and other critical design features that must be incorporated when creating CAD designs.

There are two main types of plastic keymat, one is the combination of plastic key caps with rubber keymat, called as P+R keypad or plastic and rubber keypad, and the other is pure plastic, which is mainly used in mechanical keyboard. 

Plastic Keymat Structure

Plastic Keymat come in two basic structure: conductive keymat and non-conductive keymat.

1.Conductive plastic keymat with an integral conductive carbon pill or conductive ink printing on the back side. 

Conductive plastic keymat are a single piece of molded silicone rubber incorporating visible plastic keycap into a base mat that rests against a printed circuit board and a thin key webbing of rubber between keytops and base mat.

Pressing a button on plastic keymat forces the key webbing to deform, at which point the keymat's conductive contact touches the PCB contact.

Options of conductive plastic keymat:

Carbon Pill- Conductive carbon pills are typically manufactured from a silicone conductive material that contains carbon. Conductive pills are molded into the actuators of the keys. 

Conductive Ink Printing- Conductive printing involves the deposition of conductive materials, such as ink or paste, onto a substrate to create electrical pathways. In the case of rubber keypads, conductive ink is used to form the circuitry and contact points on the keypad's surface. It has the same function with carbon pill. 

Golden Pill- Gold plated pill is used to support extremely low contact resistace requirements for keypad applied to electrical applicances and medical/health care products.

Nickel Pill- Very low resistance, but with high cost.

Black Carbon Pill

Conductive Ink Printing

2. Non- conductive plastic keymat that presses against a metal snap dome switch. Plastic keymat without conduction function is not designed with key webbing. There is no carbon pill or conductive contacts on the backside of the keymat and tactile feeling is provided by the metal snap dome or tact switch instead of force.

Non-conductive plastic keymat has the same visual appearance as conductive plastic keymat but have some significant difference in the construction.

Options of non-conductive plastic keymats:

Metal Dome.

Tact Switch.

Non-conductive Keymat

Metal Dome Plastic Keymat

To achieve good appearance of plastic keymat, characters are usually applied.

There are several solutions to form the legend on plastic keymat.

Silkscreen Printing- Printing is the most common method of marking plastic keymat. The same way as marking silicone rubber keypad.

Laser Etching- Laser etching also called as laser engraving, is especially well suited for applications when the plastic keymat is backlit.

Double-shot moulding/Dual-injection moulding- It is the process of moulding plastic around a preformed plastic insert. This has been a popular process to create durable plastic keycaps.

Double-shot moulding is a two-step process. In the first step, the legend or graphics to be placed on the keycap, are moulded in plastic. The plastic insert, resulting from the first step, is then placed into another mould and plastic is inserted under heat to combine both moulds to a single piece keycap.

Laser etching on the backside- The same process with common laser etching. The only difference is that the back of the plastic keycap is sprayed and laser etched so that the characters never come off.

Silkscreen Printed Plastic Keymat

Plastic Keymat With Raised and Printed Symbols

Double-shot Moulding Plastic Keyboard Cap 

Dual-injection Moulding Plastic Keycap for Rubber Keymat

Laser etching on the top surface of the plastic keycap

Laser etching on the backside of plastic keycap

Double-shot Moulding P+R Plastic Rubber Keymat with Keycap & Button Pad Manufacturing Process

Plastic Keymat Assembly Ways

-Combine plastic key cap with silicone button pad by assembly.

-Combine plastic key cap with silicone button pad by glue.

The manufacturing process are the same in both methods. Silicone button pad and plastic keycap are molded respectively.Silicone button pad are produce by compression molding and plastic keycap are molded by plastic injection molding.Then combine two piece by glue or just assembly together.

Manual Assembly of The Plastic Button Cap with Rubber Button Pad

Use Glue to Combine Plastic Button Cap with Silicone Button Keypad

Plastic Keymat Keycaps Material

The main material used for plastic key caps are as following:

ABS- The most common material used for plastic key. With light weight, durable, easy to process and other characteristics. ABS is hard and it is easy to carve, paint or increase the luster on the surface.

PC- Close to the transparency of PMMA, excellent heat resistance. The advantage is stable dimension, and high precision. The disadvantage is that the wear resistance is not good, not resistant to high temperature.

ABS+PC- Combined with the characteristics of ABS and PC, and improve the heat resistance and hardness of ABS.

PBT- It is good heat resistance, anti-ultraviolet, anti-oxidation, anti-wear, anti-weathering, anti-pollution and anti-corrosion. PBT is very hard and usually used for keyboard. Cost is high.

PMMA & Acylic- It has excellent transparency and good light conductivity, high mechanical strength at room temperature, but the surface hardness is low, easy to wipe, so the packaging requirements are very high.